The present invention relates generally to truck bodies and, more particularly, to aerodynamic front sections of trucks.
Motor vehicles, and in particular trucks, are a critical component of the system for transporting materials, goods and people from place to place. The amount of energy required to move such vehicles depends on many factors. For instance, a substantial amount of energy is expended to overcome the resistance encountered in moving the vehicle through air. The amount of energy expended depends in large part on the aerodynamic drag force exerted on the vehicle by the air. A vehicle moving through air experiences a drag force, which may be divided into two components: frictional drag and pressure drag. Frictional drag comes from friction generated generally through the boundary layer as the vehicle passes through the air. Pressure drag results from the net pressure forces exerted as the air flows around the vehicle. A substantial component of the pressure drag is associated with the formation of a low pressure zone behind the vehicle, as evidenced by the formation of a wake behind the vehicle.
The distinction between frictional drag and pressure drag is useful because the two types of drag are due to different flow phenomena. Frictional drag is typically most important for attached flowsxe2x80x94that is, where the flow boundary layer has not separated from the vehicle surfaces, and is related to the surface area exposed to the flow. Pressure drag dominates for separated flows, and is generally related to the cross-sectional area of the vehicle facing the air flow. When the drag on vehicle is dominated by pressure drag forces, it will expend far more energy traveling through air than the same vehicle dominated by friction drag forces. It is therefore advantageous in the design of a vehicle to reduce pressure drag forces; thereby increasing the aerodynamic properties and efficiency of the vehicle.
A bluff body, such as a conventional truck hood or front section, produces significant pressure drag at typical highway speeds. One reason for the large pressure drag is the presence of a sharp angle located at a leading edge of the truck hood. More specifically, typical truck front sections include a substantially vertical front surface or grill that meets, along an upper edge, a substantially horizontal top surface. The air flow passing over the front section, therefore, must negotiate an abrupt change in direction as the edge where the hood structure transitions from a substantially vertical orientation to a substantially horizontal orientation. This abrupt turn causes the flow to xe2x80x98separatexe2x80x99 from the top surface of the hood, forming a highly turbulent region of air located directly above the top surface of the hood, between the leading edge and the windshield.
In general, when the drag force experienced by a vehicle is dominated by pressure drag, the vehicle is considered to be bluff, and when the pressure drag is relatively small, the vehicle is considered to be streamlined. For a given truck frontal area at typical highway speeds, the pressure drag can contribute significantly to the total drag force, and therefore to the fuel efficiency (or lack thereof) of the vehicle. For example, it is well known that the drag of a cylinder can be ten times larger than a streamlined shape (such as an airfoil) having the same frontal area. It will be apparent to one skilled in the art that it is advantageous to reduce the total drag force exerted upon a vehicle by reducing pressure drag forces.
The front profile of a conventional truck is typically a bluff body. Referring to FIG. 1, a perspective view of a prior art Class 8 truck 10 showing an airstream 12 flowing over a hood 16 is depicted. The depicted air stream 12 encounters the conventionally shaped Class 8 truck 10 at the substantially vertical surface of the front surface or grill 14 of the hood 16. (It will be appreciated that for purposes of the present aerodynamic discussion, the truck""s 10 forward motion at highway speeds is equivalent to an air stream 12 having a similar but opposite velocity flowing over a stationary truck.) The air stream 12 turns upwardly as it negotiates the grill 14, and separates at a leading edge 15 of the hood 16, thereby forming a vortex or wake region 22 located aft of the leading edge 15. The airflow separation at the leading edge 15 causes the formation of a large wake region 22 and pressure losses due to eddy formation in the wake region, thereby increasing drag on the vehicle.
Furthermore, in practical applications, the air stream 12 will include ubiquitous highway particulates, e.g. road grime, which are circulated in the eddies formed in the wake region 22. The eddy driven recirculation of the grime results in an increased rate of deposition of the particulates contained in the air stream 12 upon the hood 16 and windshield 18. This results in a high rate of road film build-upxe2x80x94thus impairing the driver""s vision, and therefore safety, and increasing the amount of labor and stops required to keep the truck""s 10 windshield 18 clear, resulting in inefficiency and increased costs.
One method of reducing the bluff body characteristics of the conventional Class 8 truck and thus the resulting aerodynamic drag, is to streamline the outer contours of the front section of the truck 10. For example, in order to reduce abrupt changes in air flow over the hood, some modern truck hoods have been made to slope downwardly from the windshield toward the front of the truck, creating a less abrupt transition between the front grill 14 of the front section and the top surface of the hood 16. This more aerodynamic shape reduces the amount of flow separation, and consequently reduces the pressure drag exhibited upon the vehicle. The resulting vehicle shape, however, is significantly different from the aesthetically pleasing bluff-shape body of a conventional Class 8 vehicle. Therefore, although the resulting streamlined shape may be more aerodynamic and thus efficient, it often results in an unappealing aesthetic appearance to many truck operators and purchasers; causing a corresponding decrease in sales and loss of revenue. Further, such a design may still incorporate discontinuous regions, due to packaging for under hood components such as radiators, air ducting, or coolant tanks, that produce abrupt changes in air flow resulting in the creation of a wake region 22, again allowing road grime to be recirculated to impact and deposit upon the windshield 18 and an increase in drag.
Thus, there exists a need for an aerodynamically designed front section of a motor vehicle that mitigates drag forces and/or reduces grime build-up on the windshield while retaining the aesthetic appeal of a bluff body shape.
In accordance with one embodiment of the present invention, a truck front section comprising a grill, a hood, and a bridge assembly is provided. The grill has a substantially vertical front surface and an upper portion. The hood has an upper panel with a sloping front end disposed adjacent the grill upper portion. The bridge assembly is disposed above the front end of the hood upper panel and has a pair of oppositely disposed upright end members attached to the hood upper panel. The bridge assembly also has a substantially horizontal aerodynamically shaped member attached to the end members. The upper portion of the grill, the front end of the hood upper panel and the bridge assembly cooperatively form a duct generally disposed above the grill. The duct may be comprised of a single duct portion or multiple duct portions. The duct may discharge into a longitudinal channel formed in the upper panel. The upper portion of the grill may slope rearward. A horizontal width of an inlet of the duct may extend across substantially the entire length of the upper portion of the grill.
In accordance with aspects of another embodiment formed in accordance with the present invention, a truck hood having a front end, a rear end, and a longitudinal axis is provided. The truck hood includes an upper surface sloping downwardly from the rear end to the front end, the upper surface defining an upwardly-open, longitudinal channel. The truck hood includes a bridge assembly coupled to the upper surface and disposed at the front end of the truck hood above the upper surface, wherein the bridge assembly and the upper surface cooperatively form a duct having a generally forward-facing inlet, and an outlet in fluid communication with the upwardly-open, longitudinal channel. The duct flow area may decrease from the forward-facing inlet to the outlet. The front end of the upper surface may curve downwardly. A horizontal width of an inlet of the duct may extend across substantially the entire length of the front end of the upper surface.
In accordance with aspects of still another embodiment formed in accordance with the present invention, a front section of a vehicle having a longitudinal axis is provided. The front section includes an upper surface having a leading portion and a substantially horizontal downstream portion. The front section also includes a substantially vertical front surface coupled to the leading portion of the upper surface. The front section further includes a duct having an inlet disposed near a top end of the front surface and an outlet disposed at the downstream portion of the upper surface, wherein the leading portion of the upper surface is arcuate shaped. The front section may include an upwardly-open longitudinal channel formed in the downstream portion of the upper surface, the longitudinal channel in fluid communication with the duct outlet. The duct inlet may extend across substantially the entire length of the leading portion. The duct may converge from a first flow area measured at the inlet to a smaller second flow area at the outlet. The front section may further include a second duct and/or a second upwardly-open longitudinal channel. The upper portion of the substantially vertical front surface is rearwardly sloped to pass underneath the bridge assembly.